Mendelian Genetics

Diploid Cells
- All cells in the human body (except gametes) are diploid.
- Contain two copies of each chromosome:
- One copy from mother (in her egg).
- One copy from father (in his sperm).
Total Chromosomes: The total number of chromosomes constitutes a key aspect of genetic identity.

Gene:
- Definition: A section of DNA that provides the instructions for making a protein.
- Since a gene is a part of a chromosome, having two of each chromosome means two copies of instructions to make every protein in our bodies.
Alleles:
- Definition: Different versions of the same gene.
- Inherited a full set of chromosomes (and thus genes) from each parent but may not inherit the same version of every gene.
- Example:
- Mom gives a gene for blue eyes; dad gives a gene for brown eyes.
Homologous Chromosomes:
- Definition: Matching chromosomes from the mother and father.
- Characteristics:
- Same genes in the same locations but may contain different alleles.

Gregor Mendel:
- An Austrian monk known as the “Father of Genetics” for his work with pea plants.
3 Laws of Inheritance:
- Law of Dominance
- Law of Segregation
- Law of Independent Assortment

Control Over Breeding:
- Used pea plants that typically self-pollinate.
Use of Purebred Plants:
- Definition: Organisms whose ancestors are genetically uniform.
Observation of “Either-Or” Traits:
- Selected traits include:
- Pea shape
- Pea color
- Pod shape
- Pod color
- Plant height
- Flower color

Cross:
- Definition: The mating of two organisms.
Generations:
- P = Parental generation
- F1 = First generation
- F2 = Second generation

Letter Assignments for Alleles:
- Uppercase letters represent dominant alleles (e.g., A).
- Lowercase letters represent recessive alleles (e.g., a).
Alleles in Individuals:
- Each individual has two alleles (one from each parent) for every gene.
Homozygous and Heterozygous:
- Homozygous:
- Definition: Two of the same alleles.
- Examples: AA or aa
- Heterozygous:
- Definition: Two different alleles.
- Example: Aa

Genotype:
- Definition: The actual alleles inherited.
- Example: Genes that code for flower color, such as FF, Ff, or ff.
Phenotype:
- Definition: The physical traits/characteristics seen in an organism.
- Example: Purple flowers.

Dominant Allele:
- Definition: If present, the allele will always have that trait expressed (seen).
- Example: If brown hair is dominant over blonde hair, then:
- Let b be the allele for blonde hair.
- Let B be the allele for brown hair.
- Having B allele from one or both parents results in brown hair (either BB or Bb = brown).
Recessive Allele:
- Definition: Allele will only express its trait when the dominant allele is not present.
- Only way to express blonde hair is to have the bb genotype (inherited b alleles from both parents).

Definition: When chromosomes separate during meiosis, each gamete (egg or sperm) receives only one chromosome from each pair.
Example:
- A man with alleles for brown hair (B) and blonde hair (b) is heterozygous (Bb).
- His sperm can contain either the allele for brown hair (B) or the allele for blonde hair (b).
- Each sperm only receives one of these alleles.

Definition: The separation of chromosomes for one trait does not affect the separation of chromosomes for another trait.
Mechanism:
- Any combination of maternal and paternal chromosomes can be passed on because homologous chromosomes align randomly during metaphase.

Punnett Square:
- Definition: A diagram that shows the probability of inheriting traits from parents with certain genes.
Type of Cross:
- Monohybrid Cross: A cross between two organisms examining one trait.
Purpose: Helps visualize the possible genotypes of offspring.

In pea plants, round seeds are dominant to wrinkled seeds. Cross a homozygous recessive plant with a homozygous dominant plant.
Cross two heterozygous plants.
Cross a heterozygous plant with a plant that has wrinkled seeds.